The proposed research will be designed to elucidate the spectral cues used to locate sound in the horizontal plane when listening monaurally. The spatial referents (azimuthal positions) of bands of noise (1.0 kHz in width) will be determined for a variety of center frequencies. Then localization tests will be presented to find out how great a range of spatial referents is required for accurate performance. This range will be augmented by increasing the bandwidth. To learn if the spatial referent of a narrow band of noise of a specific center frequency is related to the filtering properties of the pinna, a miniature microphone will be placed at the entrance of the ear canal. Its output voltage in response to a series of narrow noise bands differing in center frequency will be measured. The data will be examined for a correspondence between the physical and perceptual events.